Basking sharks
Project Leader: Mauvis Gore
To hear Mauvis talking about her work on BBC Radio 4 click here. To read about the Basking Shark Workshop taking place on the Isle of Man later this year, click here.
Background
Dr Mauvis Gore
At up to 10-11 meters in length and 5-7 tonnes in weight, the basking shark (Cetorhinus maximus) is the second largest fish in world. However, as a result of fishing pressure, its global existence is now seriously threatened, with the species' total population thought to have diminished to around only 8,200 individuals.
In British waters, it is regularly seen between mid and late summer along the west coast of Scotland, where it feeds on microscopic zooplankton near the surface of the ocean, its dark dorsal fin often causing curiousity as well as a few cases of unnecessary panic. However, though regularly spotted, a major problem in its conservation and management has been that no reliable estimates of its numbers have ever been made, largely because it was assumed that the numbers seen at the sea surface were representative of the total population. It is now appreciated that these sharks also often feed at depth, with surface numbers representing only a variable portion of the total.
In British waters, it is regularly seen between mid and late summer along the west coast of Scotland, where it feeds on microscopic zooplankton near the surface of the ocean, its dark dorsal fin often causing curiousity as well as a few cases of unnecessary panic. However, though regularly spotted, a major problem in its conservation and management has been that no reliable estimates of its numbers have ever been made, largely because it was assumed that the numbers seen at the sea surface were representative of the total population. It is now appreciated that these sharks also often feed at depth, with surface numbers representing only a variable portion of the total.
In the field
Since 2004, Dr Mauvis Gore has been leading a SOSF funded research
project to quantify and qualify the population dynamics and
demographics of the basking shark in Scotland. The project is being
carried out in collaboration with the University of London Marine
Biological Station Millport (UMBSM), in the Firth of Clyde in
south-west Scotland, and in association with other environmental groups
and agencies, including the UK based Marine Conservation Society.
Aims & objectives
This SOSF funded project aims to build a comprehensive photographic
database of UK observed basking sharks, while simultaneously using
satellite tracking to observe and investigate their migratory movements
into international waters.
Read our basking shark article here and get more information about the Basking Shark Workshop taking place this year on the Isle of Man, UK.
Read our basking shark article here and get more information about the Basking Shark Workshop taking place this year on the Isle of Man, UK.
Project Update: 2008
Even before the basking shark season has begun in the UK, the project has already had some amazing results from the two tags deployed in 2007 off the Isle of Man, with one of the sharks moving north from the Isle of Man into the Clyde Sea Area, rather than continuing further north to the Hebrides.
It was the other individual however, who produced something quite extraordinary. The tagged female travelled 9,589 km to the waters off the Newfoundland shelf, and on her journey across the Atlantic Ocean managed to reach a maximum depth of 1,264 metres.
This data not only provides the deepest recorded dive depth for any tagged shark, but shows the first evidence for basking sharks utilising the deep mid-ocean and more significantly still, that the species is able to migrate across oceans or even hemispheres. This individual’s journey gives us the first tangible evidence that the European and American populations could be considered a single reproductive pool; previous to this they were always assumed to be discrete populations.
The implications from a conservation standpoint are also significant. Though basking sharks are protected in European waters, if as we now know, they are able to traverse from ocean to ocean, they could well travel into water where they have no protection. This research highlights the need for international collaboration with both governments and scientists if this vulnerable species is to have a chance of surviving.
It was the other individual however, who produced something quite extraordinary. The tagged female travelled 9,589 km to the waters off the Newfoundland shelf, and on her journey across the Atlantic Ocean managed to reach a maximum depth of 1,264 metres.
This data not only provides the deepest recorded dive depth for any tagged shark, but shows the first evidence for basking sharks utilising the deep mid-ocean and more significantly still, that the species is able to migrate across oceans or even hemispheres. This individual’s journey gives us the first tangible evidence that the European and American populations could be considered a single reproductive pool; previous to this they were always assumed to be discrete populations.
The implications from a conservation standpoint are also significant. Though basking sharks are protected in European waters, if as we now know, they are able to traverse from ocean to ocean, they could well travel into water where they have no protection. This research highlights the need for international collaboration with both governments and scientists if this vulnerable species is to have a chance of surviving.
Project Update: 2007
With background work on the relationship between the basking sharks and their zooplankton food sources completed and an effective observer network in place, priority was given to quantitative surveys, photo-identification and monitoring the movements of individuals through tagging. In all, the 2007 season was highly successful, a consequence in part of the acquisition of a new project vessel, Fairy Tern, a ‘fast-fisher’ that is small enough to maneuver around sharks and be used for tagging, yet big enough to provide basic overnight accommodation, and survive moderately rough weather. The boat has already proved invaluable, enabling the team to get out at short notice, responding to reports of sharks as they occur.
The team has also been able to take volunteers out to sea with them, and reach more of the public to raise awareness of shark conservation issues. Perhaps as a result, more basking sharks have been recorded than in previous years, with the number of sightings in Scotland this year reaching 366 between early April to early October. The largest number of sharks seen on one day was 52, recorded by the Project Basking Shark team along the east coast of the island of Coll, in the Inner Hebrides.
So far as possible, all the basking sharks encountered have been photographed, with close-up pictures of dorsal fin and, where possible caudal fin, being taken for photo-identification purposes. Besides increasing the catalogue of identifiable individuals, this has begun to provide data on the proportions of re-sightings. While a handful of the sharks identified were ones that had been recorded in the same or near-by locations within a period of weeks, the number of new sharks was considerable. Further analysis will provide information to relate the numbers of sharks recorded by the observer network to the numbers of sharks observed feeding in surface waters. Most excitingly, four satellite archival tags have been deployed, using an improved attachment method, and have been generating data. The tags provide information on the depth and temperature profiles of the sharks, as well as their locations throughout the time the tag is attached. Two of the tags were deployed off the Isle of Man in collaboration with DAFF (Isle of Man Department of Agriculture, Fisheries & Forestry) and the Manx Wildlife Trust and Marine Conservation Society-sponsored Basking Shark Watch. The two remaining tags were deployed off the Isle of Coll, on the Scottish west coast, and should down-load their data by late November 2007. This will provide further insightful data into the behavior and dispersion of this key population of basking sharks.
The team has also been able to take volunteers out to sea with them, and reach more of the public to raise awareness of shark conservation issues. Perhaps as a result, more basking sharks have been recorded than in previous years, with the number of sightings in Scotland this year reaching 366 between early April to early October. The largest number of sharks seen on one day was 52, recorded by the Project Basking Shark team along the east coast of the island of Coll, in the Inner Hebrides.
So far as possible, all the basking sharks encountered have been photographed, with close-up pictures of dorsal fin and, where possible caudal fin, being taken for photo-identification purposes. Besides increasing the catalogue of identifiable individuals, this has begun to provide data on the proportions of re-sightings. While a handful of the sharks identified were ones that had been recorded in the same or near-by locations within a period of weeks, the number of new sharks was considerable. Further analysis will provide information to relate the numbers of sharks recorded by the observer network to the numbers of sharks observed feeding in surface waters. Most excitingly, four satellite archival tags have been deployed, using an improved attachment method, and have been generating data. The tags provide information on the depth and temperature profiles of the sharks, as well as their locations throughout the time the tag is attached. Two of the tags were deployed off the Isle of Man in collaboration with DAFF (Isle of Man Department of Agriculture, Fisheries & Forestry) and the Manx Wildlife Trust and Marine Conservation Society-sponsored Basking Shark Watch. The two remaining tags were deployed off the Isle of Coll, on the Scottish west coast, and should down-load their data by late November 2007. This will provide further insightful data into the behavior and dispersion of this key population of basking sharks.